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Friday, October 29, 2010

At the moment, news for future planetary missions is scarce as the U.S. waits for the results of the Decadal Survey. (Other nations continue their own planning cycles, but news is scarce there, too.) The Decadal Survey has published a list of 25 missions it is considering for the next decade. I thought that I would take the next few blog entries to pick the five missions from that list that I find most compelling. I'm under no illusion that I will persuade anyone (especially anyone who influences government spending). However, I find a well argued (and I hope these will be) argument to help me form my own opinions. Please provide your opinions, too, in the comments. You can find the first installment in this series at Thoughts on the Most Compelling Proposed Planetary Mission.

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We live on a terrestrial planet, and one on which we are undertaking a grand experiment to see what happens when we dramatically increase the proportion of greenhouse gases in the atmosphere. As a result, I think that furthering our understanding of Venus as a terrestrial planet and a greenhouse atmosphere carried to extremes is a compelling target for exploration in the next decade, and is for me, the target for the second most compelling mission for the coming decade.

Venus has been essentially ignored by NASA spacecraft for over 15 years (brief studies by spacecraft en route to other worlds have been the only exceptions). The Europeans and Japanese, however, have sent orbiters to this world, and the Russians are planning a mission in the coming decade that may include a lander, orbiter, and balloon. I believe that the U.S. should join the party in the coming decade.

The VEXAG analysis group chartered by NASA has put together an ambitious plan for a highly sophisticated Venus Flagship mission. This mission would include a very capable orbiter, two balloon platforms, and two atmospheric probes/landers that would survive for many hours on the surface for detailed soil analysis. Unfortunately, this mission would cost over $3B and requires technology development in several areas. As a result, it is proposed as a mission for the 2020s and not the coming decade.

However, VEXAG members have also proposed a less capable mission, the Venus Climate Flagship, as a possible mission for this coming decade. In the types of mission elements -- an orbiter, a single balloon, and a single lander -- it seems much like the full Venus Flagship proposal with the duplicate platforms removed. However, the Climate Flagship would focus on using existing technology, resulting in less capable measurements but doing them as much as a decade sooner. For example, the full Flagship mission would have brought samples into the landers for analyses that would take several hours to complete. This would result in expensive sample handling mechanisms, an air lock, and the requirement to survive on the surface for almost a full Earth day. The Climate Flagship proposal, on the other hand, would use lasers to illuminate or melt the surface materials with the results analyzed via spectrometry through a porthole in less than an hour. Similarly, the full Flagship proposal would have carried a radar on the orbiter that would have mapped the surface with resolutions as fine 5 m. The Climate Flagship would map the surface at "10X" better resolution than the Magellan mission. This would result in mapping resolutions of several 10s of meters. (The exact figure depends on whether average or best Magellan resolution would be the baseline, and it's likely that the Climate Flagship proposal hasn't been studied in sufficient detail that the final resolution is known.)

There isn't a firm public estimate for the cost of the Climate Flagship. A swag in the presentation describing the mission suggests a figure of ~$1.6B, but notes that your "mileage may vary." However, with international cooperation, the NASA contribution might be substantially less. Several nations are interested in missions to Venus. Russia, for example, wants to fly its Venera-D lander this decade. The Europeans have expressed interest in flying a balloon platform. NASA might contribute an orbiter for data relay from landers and balloons, to remap portions of the surface with radar at higher resolutions, and carry cameras and imaging spectrometers to extend the atmospheric and surface studies of the European Venus Express and Japanese Akatsuki orbiters. The RAVEN radar mission has been proposed for the current Discovery mission selection. NASA also might contribute a lander if the SAGE mission is selected as the next New Frontiers mission.

The Decadal Survey has three flavors of landers and a "climate mission" (no details on what that might include) on its list of candidate missions it is considering. If any of these missions are recommended, or if the SAGE lander is selected, NASA could participate a series of missions that would perform the science of the Climate Flagship. (I think it is unlikely that the Decadal Survey would recommend the entire Climate Flagship mission, which as its cost become better understood, might be substantially more expensive than the swag quoted above.) The Survey could recommend a single element -- the orbiter or a lander -- or a combination such as an orbiter and atmospheric probe. It could also recommend no NASA-led mission, and instead recommend participation in the missions of others. The Russians, Europeans, and Japanese could supply missions that meet the goals of the Climate Flagship. China and India are also on the verge of being able to send probes to other planets and might also participate.

Except for the recent European and Japanese orbiters, our knowledge of Venus is based on missions with decades old technology. The science questions motivating a return to Venus seem compelling to me. I believe that NASA should make continued exploration -- preferably as part of an international effort -- a priority for the coming decade.

Meteorite-Based Debate Over Martian Life Is Far from Over (space.com) - The debate over whether meteorite ALJ84001 from Mars has signs of past Martian life continues. This suggests how hard it will be to detect signs of life even in returned samples. (While I've come to favor a Martian sample return mission, it's not because I think it will settle the question of past life on Mars, but for what it will tell us about the earliest history of processes on terrestrial worlds.)

Two articles focus on how the James Webb Space Telescope came to dominate NASA's astronomy program and what the effects will be. This is a cautionary tale about what happens when Decadal Surveys prioritize a mission the ends up costing far more than expected. The lesson was learned -- both the recently completed Astronomy and the in-progress Planetary Decadal Surveys put a strong focus on attempting to cost out missions in more detail than was done for the previous round of Surveys.

Wednesday, October 20, 2010

At the moment, news for future planetary missions is scarce as the U.S. waits for the results of the Decadal Survey. (Other nations continue their own planning cycles, but news is scarce there, too.) The Decadal Survey has published a list of 25 missions it is considering for the next decade. I thought that I would take the next few blog entries to pick the five missions from that list that I find most compelling. I'm under no illusion that I will persuade anyone (especially anyone who influences government spending). However, I find a well argued (and I hope these will be) argument to help me form my own opinions. Please provide your opinions, too, in the comments.

There are many ways to decide on what would be a compelling mission. One would be on the vicarious thrill of exploration. On this basis, I would favor missions such as the Venus SAGE lander, the AVIATR Titan plane, and the Argo Neptune-Triton-KBO mission. (All would also provide great science.) However, nations chose to fund these expensive mission primarily on their scientific return. So I have taken that as my criteria. Which set of missions would most fundamentally advance our understanding of the solar system?

A recent paper in the scientific journal Astrobiology, New Priorities in the Robotic Exploration of Mars: The Case for In Situ Search for Extant Life (subscription or purchase required), has got me rethinking the priority for a Mars sample return. Mars has been the major focus of NASA's planetary program for the last 15 years. With the recent cooperative agreement, it has also become a major focus for ESA. Review board after review board for the last 30 years have concluded that the highest priority for Mars exploration is to return samples to Earth (see, for example, the 2003 Decadal Survey report). The mission has been recommended for flight at the earliest opportunity, but NASA's budgets have never permitted the mission to begin development.

There have been scientists who recommend a slower approach. Mars is highly diverse and we have explored its surface in only six places, and landing safety concerns limited our choice of places to explore. Samples of past or present life are likely to be hard to find. Instead of rushing to a sample return, these scientists argue, fly a number of landed missions, probably most of them rovers, to find the best place to return a sample. This, in a nutshell, is the argument the authors make in the New Priorities in the Robotic Exploration of Mars paper.

At least based on presentations at meetings and the roadmap adopted by the Mars science community (principally through MEPAG), this appears to be a minority view. Most of the community apparently has decided that we know enough about Mars to pick a very interesting site. The samples returned from that site when analyzed with Earth-based instruments (most of which would be larger than the rover collecting the sample and some of which would be larger than the launch vehicle -- size and power counts for sophisticated study at the scale of individual rock grains) would greatly deepen our understanding of the early history of terrestrial planets. Only Mars preserves that early history on a body that had both a significant atmosphere and liquid water.

Long term readers of this blog know that I am a skeptic on Mars sample return. Not because I don't think the science is absolutely compelling -- it is -- but rather because I doubt that Congress will fund a $6B+ program for robotic exploration. I've come to reevaluate that position, though. Congress has funded the James Webb Space Telescope to the tune of over $5B (but at the cost of the astronomy program foregoing many other missions). Also, events seem to make this the time to move forward:

Fifteen years of missions by NASA and ESA to Mars have revolutionized our understanding of the Red Planet. We may not be able to pick THE most compelling site on Mars, but we can pick A (and actually several) very compelling sites.

JPL has developed for the Mars Science Laboratory the entry, landing, and roving technology essential to carry out this type of mission. (Of course, it also hasn't been flight tested...) If NASA does not continue a program to use this technology, the key engineers will move on to other projects. As it is, waiting seven years between the launch of MSL and the proposed Max-C sample caching rover is stretching the period over which teams can be kept together.

The opportunity to fly the caching rover with the ExoMars in 2018 rover is unique. ExoMars can allow samples to be collected from up to two meters below the surface while Max-C collects samples at the surface. This could greatly enhance the value of the returned samples.

ESA has agreed to partner with NASA on a sample return (exact roles and funding levels to be determined). This offers an opportunity to share costs that may not come again.

So, I have come to decide that moving towards a Mars sample return with the 2018 Max-C rover/ExoMars mission is the most compelling mission to me on the list of missions under consideration by the Decadal Survey. This mission depends on an orbiter being launched by 2016 to act as a communications relay; the Mars Trace Gas Orbiter is currently slotted for this role. Together, the two missions would cost NASA probably $3B, perhaps as much as $4B with inflation and cost overruns (ESA would also make a substantial contribution for the orbiter and the ExoMars rover). This would represent a quarter to a third the expected NASA planetary mission funding for the next decade.

There is the risk that the current estimates for cost will turn out to be wildly optimistic and the true costs will eat up a large portion of the planetary science budget. After approval, politicians could cancel the mission to save money. It happened with the Venus Orbiting Imaging Radar mission in 1981 (the eventual Magellan mission was less capable), the Comet Rendezvous and Asteroid Flyby mission (ESA's Rosetta eventually filled this slot), and almost happened to the Galileo mission.

Given these risks, I favor a go slow approach. Fly the Max-C and ExoMars rover in 2018. Wait until we know there is a compelling set of samples waiting on the surface for pickup before committing to the next mission in the sequence (see this blog entry for a description of the three missions needed to return a sample to Earth). If the 2018 mission fails or is skunked, launch another rover to find and cache a compelling set of samples. Under this approach, the earliest a sample could be returned would probably be 2028 (instead of the current strawman for 2026).

Going with a sample return mission isn't without its risks, both technically and politically. However, the return seems to me to be greater than any other mission on the list.

Monday, October 11, 2010

Note: We appear to be in a quiet time for planning future planetary missions. In the U.S., we are awaiting the recommendations of the Decadal Survey to be released next March. In Europe, we are waiting for the decision for the next large mission selection between a Jupiter Ganymede orbiter and two astronomy missions. I will post as information and ideas become available, but I expect that posts may occur every week or so for awhile.

One of the most exciting concepts for a future planetary mission has been a mission to land on and sample one of the large lakes of Titan. The lakes are likely to be chemical repositories that contained important clues to Titan's "are repositories, through dissolution of airborne solids, of organics scattered globally on Titan, as well as noble gases, which are a key clue to Titan’s origin and evolution." Sampling the lakes will help answer important questions about Titan:

Cassini-Huygens leaves us with many questions that require a future mission to answer. These include whether methane is out-gassing from the interior or ice crust today, whether the lakes are fed primarily by rain or underground methane-ethane aquifers (more properly, “alkanofers”), how often heavy methane rains come to the equatorial region, whether Titan’s surface supported vaster seas of methane in the past, and whether complex self organizing chemical systems have come and gone in the water volcanism, or even exist in exotic form today in the high latitude lakes." [NASA/ESA JOINT SUMMARY TITAN SATURN SYSTEM MISSION, January 2009]

As part of its analysis of missions to recommend in the coming decade, the Decadal Survey commissioned a study of possible Titan lake probe missions. The results of the analysis was presented at a recent conference, and the studies' lead, John Elliott of JPL was kind enough to send me a copy of the presentation and answer some questions.

The study looked at addressing four key scientific questions using variations of two variations of probes that would sample one of Titan's large northern lakes. The scientific questions were:

SGa: Atmospheric evolution (studied during descent through the atmosphere and by analyzing the lake)

SGb: Lake and atmospheric interaction to determine how the two exchange material much as the Earth's hydrosphere and atmsphere influence each other (studied by a long-lived floater on the surface of a lake)

SGc: Lake chemistry (studied by either a floater or a submersible)

SGd: Interior structure (studied by a long-lived submersible on the lake bottom to determine whether or not there is a large ocean deep beneath the surface as there is at Ganymede and Europa)

The study looked at a Flagship class (multiple billions of dollars) and three New Frontiers class (~$650M) missions. Only the Flagship class mission would be able to address all questions. It would place a long lived, plutonium-powered (via ASRGs) floater on the lake surface to study long term interactions and would deploy a submersible to the lake bottom for a thirty day stay before popping to the surface for data relay. The presence of an interior ocean would be explored by measuring the depth of the lake from the lake bottom using an echo sounder. The amplitude and phases of the lake tides would be used to infer the presence of an interior ocean.

The three New Frontiers missions would conduct subsets of the Flagship mission:

Long lived floater (ASRG powered) to study atmospheric evolution, lake/atmospheric interaction, and lake chemistry. Communications would be direct to Earth and the carrier craft would be a simple stage attached to the entry shell, much like the carrier craft for NASA's Martian landers.

A battery-powered submersible to study atmospheric evolution and lake chemistry. The submersible would remain on the lake bottom for only six hours before returning to the surface to relay its data back to the carrier stage for retransmission to Earth. (The presentation notes that this option would provide the most science for the dollar.)

A battery-powered floater that would survive on the lake surface for twelve hours to study atmospheric evolution and lake chemistry. (The presentation notes that this would be the cheapest option.)

In addition to options for the lake probe, the mission also had multiple options for arriving at Titan and for relaying data. One option would be to arrive at Titan by 2026 to enable direct transmission of data to Earth. This option requires launch by 2020, and to achieve this short (for a Saturn mission) transit, the carrier would require substantial fuel to enable two deep space maneuvers. A second option would be two launch by 2023 and arrive by 2032. In this latter case, data relay would have to be through the carrier, which the study assumes would be ASRG powered. (Elliot told me that solar powered carriers might be an option, but, "but there are a lot of unknowns (e.g. required technology developments) and uncertainties in how much array area we’d need and how well cells would perform at Saturn distances, etc., so we chose for the study to assume ASRGs as the simpler implementation given our current understanding. This is something that could benefit from a more detailed trade if further studies are performed.")

The TIME Discovery proposal that is been discussed in this blog would most resemble the long-lived floater concept with direct communication to Earth and a dumb carrier. The TIME mission assumes a launch by the mid portion of this decade, possibly eliminating the need for powered deep space maneuvers. The Discovery proposal also would benefit from NASA providing the ASRG's outside the mission's PI budget of ~$450M, enabling the mission to potentially fit within that lower budget instead of a New Frontier budget (~$650M).

Tuesday, October 5, 2010

Mapping the surface of Titan is hard. The smoggy atmosphere scatters most wavelengths of light. The depth of the atmosphere prevents spacecraft from getting close enough for high resolution images. Radar offers an alternative to optical imaging, but the equipment necessary is heavy, power hungry, and produces large amounts of data that must be transmitted back to Earth. Resolution can also be a problem. The Cassini radar system, which uses the spacecraft's large main antenna, has a maximum resolution of 350 m at closest approach. The Huygen's landing area with its networks of hills and channels is a bright blur at these resolutions.

A recent presentation at the EPSC2010 conference, offers an alternative. The Cassini VIMS instrument discovered a clear window in Titan's atmosphere at 5 microns, which is in the infrared region of the spectrum. The authors propose a camera that would utilize that window to image Titan. From a spacecraft flying by Titan, 100 images covering 1.25% of the surface could be taken. Best resolution would be less than 50 m as the spacecraft swoops below ~2300 km above the surface during closest approach. That would provide sufficient detail to study the surface geomorphology in detail. The channels at the Huygen's landing site, for example, would be seen. (Cassini's infrared instrument, VIMS, was not optimized for spatial mapping and produces images with a maximum resolution of ~1 km.)

The lead author on the EPSC2010 abstract, Chrstophe Sotin of JPL, is also lead author of an abstract for the upcoming Division of Planetary Studies conference. The second abstract provides a brief description of the goals for a conceptual mission called JET, a Journey to Enceladus and Titan. The goals listed are high mass resolution spectroscopy of the material in Enceladus' geysers and Titan upper atmosphere to determine composition, high resolution thermal mapping of the Enceladus' tiger stripes that are the source of the geysers, and imaging of Titan's surface (presumably with the camera described above).

Editorial Thoughts: The proposed Flagship Titan orbiter would have used the 5 micron band to map the entire moon at resolutions of around 50 m. The abstract summarized above made it clear that the authors are proposing their instrument for a spacecraft that would flyby Titan, presumably while in orbit around Saturn. The area covered in detail at closest approach would be approximately one million square kilometers, a respectable area. (France is 547,030 sq. km.) It's not clear from the abstract how much of that area would be imaged at resolutions of 50 m or less. By carefully choosing the areas to be imaged to include high priority sites, such an imager should make key contributions to our understanding of Titan's surface and the processes creating it. While the authors don't discuss it, the imager should be able to image additional areas of Titan at lower resolutions from greater distances.

The imager that had been proposed for the Titan Flagship mission would have been more capable than the camera discussed here. It too would have imaged the surface at 50 m resolution, but would have used an additional transparent band in the atmosphere to provide color images (at 2.0, 2.7, and 5 μm) that could provide compositional information. The Flagship instrument also would have provided spectroscopy in the 0.85 –2.4 μm and 4.8–5.8 μm bands at 250 m resolution. (The lower wavelengths, however, would have been subjected to greater scattering by Titan's atmosphere, reducing resolution. The 5 micron band would provide the clearest images.)

I am hoping that the Decadal Survey prioritizes a New Frontiers class-Saturn orbiter to study Enceladus and Titan in the coming decade. Such a mission could carry a small suite of instruments optimized to studying these bodies. At Titan, a capable mass spectrometer could study the composition of the upper atmosphere while ice penetrating radar could study the near subsurface structure. (The JET abstract does not mention an ice penetrating radar.) Both instruments would also be essential for Enceladus studies. The 5 micron camera presented here might be a Titan-specific instrument, although this could be a channel on a high resolution thermal imager. The abstract authors don't present any information on their instrument's mass and cost. The Flagship instrument, however, had a proposed mass of 28 kg, which suggests an instrument that may have costs and mass incompatible with a New Frontiers class mission. Presumably, this is the reason that the authors of this abstract are proposing a simpler instrument focused only on imaging in one band. (I use remote sensing in my research; it would be great if this type of instrument could also image in additional wavelengths. Color images are a great tool for exploring composition with carefully selected wavelengths (as the Landsat imagers demonstrate for Earth studies).) However, even images in one band would present a big step forward in our ability to study Titan.

Sunday, October 3, 2010

A reader posted a question on my blog entry, Update on NASA's Planetary Program. I thought that the answer might interest a number of readers.

Al wrote,

You stated

"My take on the "highly restricted" and "tough choices" is that one of the two flagship class missions widely discussed -- the MAX-C Martian rover and the Jupiter Europa Orbiter -- may not be recommended. If so, I'd place my bet on a Martian rover being recommended..."

If true, could that open up the possibility of a scaled down lower cost Europa mission (Frontier class), perhaps limited to a short duration study of Europa itself and not the entire Jupiter system? Although I am a huge proponent of EJSM, I would still be thrilled to get a limited Europa focused mission, especially if it could arrive there before 2027 (ideally 2018 or so).

For convenience, I'll call this limited mission the Icy Moons Observer (IMO). It appears that it is possible to fly a mission to the Jovian system for studies of the Galilean moons at Discovery mission (~$450 M) -- the Io Volcano Observer -- or New Frontiers (~$650 M) -- ESA's Jupiter Ganymede Orbiter -- costs. Either of these concepts probably could be stretched to include a number of flybys of Europa in addition to other targets without busting the budget too badly. (Note: The Io mission would have the wrong instruments to study an icy moon, but the spacecraft design could be refitted with appropriate instruments.)

One could imagine an IMO mission that has multiple encounters with all the icy Galilean moons. A number of Europa flybys (a dozen? twenty?) could carry out global and regional surveys of that moon. Then the spacecraft might enter Europan orbit for a lifetime of a month or two (compared to the nine months plus of the proposed Jupiter Europa Orbiter Flagship mission) to carry out detailed measurements of selected locations.

I don't know, however, if a Europa orbiter can fit into either a New Frontiers or even a small Flagship (~$1B) class mission. A mission that enters Europa orbit will end with the spacecraft crashing on that moon's surface. To ensure that Earth organisms don't contaminate Europa, stringent planetary protection design and assembly requirements would have to be taken. This would step up the costs by some increment (that's unknown to me). Also, staying in orbit even for a month or two would greatly increase the radiation dose the spacecraft would suffer compared to a mission that only had flybys. This would result in another step function in mission costs.

So an IMO mission that focuses on flybys of Europa and possibly orbiting one of the further moons (probably Ganymede) certainly seems doable. A mission that orbits Europa even for a short time may or may not be doable within a constrained budget.

Saturday, October 2, 2010

The Venus (VEXAG), Mars (MEPAG), outer planets (OPAG), and small bodies (SBAG) assessment groups all met in the last month. This kind of concurrency in these meetings is unusual and presents an opportunity to provide an update on future missions across the entire range of solar system (ex the sun itself). What follows are key tidbits gleaned from the presentations that have been posted on the web (see below for links).

Steven Squyres presented an update on the Decadal Survey at the MEPAG meeting. Squyres reported that the first draft of the report and recommendations has been written an submitted for review. To quote directly from his presentation:

(Editorial note: My take on the "highly restricted" and "tough choices" is that one of the two flagship class missions widely discussed -- the MAX-C Martian rover and the Jupiter Europa Orbiter -- may not be recommended. If so, I'd place my bet on a Martian rover being recommended. To not do so would effectively end a very successful two decades of Martian exploration and lead to JPL losing the expertise it's built up on Martian entry, landing, and descent and rover technology.)

The first public release of the Survey's recommendations and report will occur at the Lunar and Planetary Science Conference next March 7-11.

While not in the presentations, NASA does not have an approved budget for FY11, which began on October 1. Congress is late with almost all appropriation bills this year, leaving NASA to operate on a continuing resolution. Frequently when this happens, a large number of agencies receive their final budgets as part of an omnibus bill. Usually, the new budget ends up looking much like the previous year's budget since there is not the time to consider each agency in detail. For planetary explortion, this could represent a loss of the substantial budget increase (~11%) in the President's proposal submitted to Congress earlier this year. Carried forward through the next decade, this increase could almost pay for an additional New Frontiers mission. (You may have heard that Congress recently approved NASA's "budget." This was actually an authorization bill, which is a policy statement on Congress' goals for the agency, which is critical given the changes in the manned spaceflight program this year. Funds are actually appropriated in seperate spending bills.)

Funding for the restart of plutonium-238 was requested in the President's budget proposal, with costs to be equally shared by NASA and the Department of Energy (DoE). The Senate's version of the DoE budget would require NASA to carry the entire $75-90 M cost. If the eventual Congressional appropriation goes with the recommendation, NASA looking to cover the entire cost out of its budget, but "significant impact to several programs will be felt."

NASA continues to move forward to enable the Jupiter Europa Orbiter if it is recommended by the Decadal Survey. The radiation and planetary protection concerns (the spacecraft would eventually crash into the surface of Europa, and NASA doesn't want to contaminate it with Earth organisms) makes instrument designs especially challenging. In an unusual step, NASA will hold a two stage selection for instruments. In the first stage, it will select two or more concepts proposed by researchers for each instrument category. Those concepts will then receive funding for end-depth design work leading to a final selection.

NASA received several dozen proposals to consider for its next Discovery mission selection, indicating that the scientific community is not running out of ideas for relatively low cost missions.

Jim Green, director of NASA's Planetary Science Division included a list of upcoming events in his presentations to the different meetings (the OPAG version is given below). Interestingly, the OPAG version suggests that the Opportunity rover will reach Endeavour crater early 2012 while the VEXAG version suggests that the arrival will be in mid-2011.

About Me

You can contact me at futureplanets1@gmail.com with any questions or comments.
I have followed planetary exploration since I opened my newspaper in 1976 and saw the first photo from the surface of Mars. The challenges of conceiving and designing planetary missions has always fascinated me. I don't have any formal tie to NASA or planetary exploration (although I use data from NASA's Earth science missions in my professional work as an ecologist).
Corrections and additions always welcome.